1. Field of the Invention
The invention relates to a fingerprint input module, more particularly to a fingerprint input module having an improved assembly accuracy and an increased yield.
2. Description of the Related Art
Referring to FIG. 1, a conventional fingerprint sensing system 1 disclosed in U.S. Pat. No. 5,796,858 includes a light source 11 for emitting light, a sheet prism 12, and an image-capturing unit 13. The sheet prism 12 includes a plurality of prismlets 121 extending in identical directions and a sensing surface 122 for contacting a finger to be sensed. The image-capturing unit 13 includes a lens 131 for collecting the light reflected from the sheet prism 12, and a detector array 132 for transforming the light from the lens 131 into an image signal. When the light from the light source 11 illuminates the finger disposed on the sensing surface 122 through the sheet prism 12, the light illuminating the grooves of the finger is reflected from the sensing surface 122 to the image-capturing unit 13 through total internal reflection, and the light illuminating the ridges of the finger will be absorbed by the finger. The light reflected from the sensing surface 122 is focused by the lens 131 to create a fingerprint image, which is dark where there are ridges and bright where there are grooves, on the detector array 132.
However, in the conventional fingerprint sensing system 1, in order to permit the light from the light source 11 to be refracted into the prismlets 121 at accurate angles for creating the total internal refection, the assembly angle of the light source 11 is strictly limited. Furthermore, in order to permit the light reflected from the sensing surface 122 through the total internal reflection to enter into the image-capturing unit 13 at an accurate angle for preventing aberrations, the assembly angles of the lens 131 and the detector array 132 should also be strictly limited. Therefore, the yield of the fingerprint sensing system 1 may be reduced due to the error of the assembly angles of the light source 11, the lens 131, and/or the detector array 132.